man-pages/man2/wait4.2

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.\" (c) 1993 by Thomas Koenig (ig25@rz.uni-karlsruhe.de)
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.\" Modified Sat Jul 24 13:32:44 1993 by Rik Faith (faith@cs.unc.edu)
.\" Modified Mon Jun 23 14:09:52 1997 by aeb - add EINTR.
.\" Modified Tue Jul  7 12:26:42 1998 by aeb - changed return value wait3
.\"
.TH WAIT4 2  1997-06-23 "Linux" "Linux Programmer's Manual"
.SH NAME
wait3, wait4 \- wait for process termination, BSD style
.SH SYNOPSIS
.nf
.B #include <sys/types.h>
.B #include <sys/time.h>
.B #include <sys/resource.h>
.B #include <sys/wait.h>
.sp 2
.BI "pid_t wait3(int *" "status" ", int " options ,
.BI "      struct rusage *" rusage );
.sp
.BI "pid_t wait4(pid_t " pid ", int *" status ", int " options ,
.BI "      struct rusage *" rusage );
.fi
.SH DESCRIPTION
The
.B wait3
function suspends execution of the current process until a child has
exited, or until a signal is delivered whose action is to terminate
the current process or to call a signal handling function.  If a child
has already exited by the time of the call (a so\-called "zombie"
process), the function returns immediately.  Any system resources used
by the child are freed.

The
.B wait4
function suspends execution of the current process until a
child as specified by the
.I pid
argument has exited, or until a signal is delivered whose action is to
terminate the current process or to call a signal handling function.
If a child as requested by
.I pid
has already exited by the time of the call (a so\-called "zombie"
process), the function returns immediately.  Any system resources used
by the child are freed.

The value of
.I pid
can be one of:
.IP "< \-1"
which means to wait for any child process whose process group ID is
equal to the absolute value of
.IR pid .
.IP \-1
which means to wait for any child process; this is equivalent to
calling
.BR wait3 .
.IP 0
which means to wait for any child process whose process group ID is
equal to that of the calling process.
.IP "> 0"
which means to wait for the child whose process ID is equal to the
value of
.IR pid .
.PP
The value of
.I options
is a bitwise OR of zero or more of the following constants:
.TP
.B WNOHANG
which means to return immediately if no child is there to be waited
for.
.TP
.B WUNTRACED
which means to also return for children which are stopped, and whose
status has not been reported.
.PP
If
.I status
is not
.BR NULL ,
.B wait3
or
.B wait4
store status information in the location pointed to by
.IR status .
.PP
This status can be evaluated with the following macros (these macros take
the stat buffer (an \fBint\fR) as an argument \(em not a pointer to the
buffer!):
.TP
.BI WIFEXITED( status )
is non\-zero if the child exited normally.
.TP
.BI WEXITSTATUS( status )
evaluates to the least significant eight bits of the return code of
the child which terminated, which may have been set as the argument to
a call to
.B exit()
or as the argument for a
.B return
statement in the main program.  This macro can only be evaluated if
.B WIFEXITED
returned non\-zero.
.TP
.BI WIFSIGNALED( status )
returns true if the child process exited because of a signal which was
not caught.
.TP
.BI WTERMSIG( status )
returns the number of the signal that caused the child process to
terminate. This macro can only be evaluated if
.B WIFSIGNALED
returned non\-zero.
.TP
.BI WIFSTOPPED( status )
returns true if the child process which caused the return is currently
stopped; this is only possible if the call was done using
.BR WUNTRACED .
.TP
.BI WSTOPSIG( status )
returns the number of the signal which caused the child to stop.  This
macro can only be evaluated if
.B WIFSTOPPED
returned non\-zero.
.PP
If
.I rusage
is not
.BR NULL ,
the
.B struct rusage
as defined in
.I <sys/resource.h>
it points to will be filled with accounting information.  See
.BR getrusage (2)
for details.
.SH "RETURN VALUE"
The process ID of the child which exited, \-1 on error
(in particular, when no unwaited-for child processes
of the specified kind exist)
or zero if
.B WNOHANG
was used and no child was available yet.
In the latter two cases
.I errno
will be set appropriately.
.SH ERRORS
.TP
.B ECHILD
No unwaited-for child process as specified does exist.
.TP
.B EINTR
if
.B WNOHANG
was not set and an unblocked signal or a
.B SIGCHLD
was caught.
.TP
.B EINVAL
Invalid value for
.I options
given for wait4.
.SH NOTES
Including
.I <sys/time.h>
is not required these days, but increases portability.
(Indeed,
.I <sys/resource.h>
defines the
.I rusage
structure with fields of type
.I struct timeval
defined in
.IR <sys/time.h> .)
.LP
The prototype for these functions is only available if
.B _BSD_SOURCE
is defined (either explicitly, or implicitly, by not defining
_POSIX_SOURCE or compiling with the -ansi flag).
.SH "CONFORMING TO"
SVr4, POSIX.1
.SH "SEE ALSO"
.BR getrusage (2),
.BR signal (2),
.BR wait (2),
.BR signal (7)